foo.cc: In function 'int main()':
foo.cc:15:35: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   15 |                 for(int j = 0 ; j < x[i].size() ; ++j)
      |                                 ~~^~~~~~~~~~~~~
foo.cc:20:35: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   20 |                 for(int j = 0 ; j < y[i].size() ; ++j)
      |                                 ~~^~~~~~~~~~~~~

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